Japanese Doubts Over the Credibility of the Current Extended Deterrence Select Japanese politicians have discussed the need for NATO-style nuclear sharing in Japan as early as 2016. This became a more well-known conversation when ex-Prime Minister Abe publicly reintroduced the topic after Russia invaded Ukraine. PM Abe commented “Japan is a signatory to the Nuclear Non-Proliferation Treaty and has its three non-nuclear principles, but it should not treat as a taboo discussion on the reality of how the world is kept safe,’ on a Japanese TV.” Japan is currently under U.S. extended nuclear deterrence, colloquially called the U.S. nuclear umbrella. The U.S. extended nuclear deterrence to Japan promises U.S. nuclear retaliation against an adversary’s nuclear attack on Japan. As the security landscape is shifting – reflected by increasing Chinese aggression – the value and validity of the U.S. nuclear umbrella is increasingly questioned. Japanese leaders like former LDP Secretary-General Toshimitsu Motegi and Kawano Katsutoshi, the chief of Japan’s Self-Defense Forces’ Joint Staff under the Abe administration have publicly doubted the credibility of the U.S. extended deterrence as to whether the United States is truly committed to retaliating against adversaries that use nuclear weapons against U.S. allies. Especially, because the retaliation can escalate to endangering the U.S. homeland. This article examines a hypothetical scenario in which the United States shares tactical nuclear weapons with Japan to deter or minimize potential Taiwan contingencies by China. If the United States decides to reintroduce tactical nuclear weapons to Japan — reminiscent of the Cold War era — what kind of tactical nuclear weapons are best suited for Japan? This paper does not promote U.S. nuclear sharing with Japan. It merely explores the feasibility of such decision. NATO-Style Nuclear Sharing Would Allow Japan To Have a Bigger Voice NATO-style nuclear sharing allows Japan to host U.S. nuclear weapons within its territory. With NATO-style nuclear sharing, the United States control all nuclear forces on allied territory. The deployment of U.S. nuclear weapons with U.S. control over them is in full compliance with the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). However, it would allow the U.S. allies to have a bigger voice in the decision-making and conduct the operations in nuclear missions (if led to escalation). Though it is not a sharing of nuclear weapons themselves as the weapons themselves belong to the United States solely, it would bestow Japan with more political and military responsibilities. Nuclear Sharing to Japan During the Cold War During the Cold War, it was suspected that the United States had tactical nuclear weapons on Japanese land or was prepared to station them there. A de-classified Far East Command Pentagon document indicates 13 locations in Japan — including Chichi Jima, Iwo Jima, and Okinawa — hosted nuclear weapons or components of or were to receive nuclear weapons in case of contingencies to counter the growing North Korean (DPRK’s) threats and the Chinese involvement on the Korean Peninsula. The U.S. government was aware that deploying nuclear weapons on Japanese islands may be key to deterring, winning, or de-escalating the conflict in East Asia. Scenarios That Could Prompt Nuclear Sharing to Japan The likelihood of the following scenarios unfolding could motivate the United States and Japan to move forward with tactical nuclear sharing as deterrence measurements against the following contingencies: China deciding to seize Taiwan either by military force, blockade, or a combination of both. Japan getting involved in a Taiwan conflict or any contingencies in nearby waters. China threatens to or invades Japan such as attacks on Japanese southern or contested islands by Chinese amphibious forces. The alliance agreeing on nuclear sharing in before any conflict happens given the rising tension in the Indo-Pacific. Credibility Against the Chinese A2AD Since the threat environment in East Asia has dramatically changed since the Cold War, thinking about nuclear sharing with Japan. Such operations now must consider China’s emerging capabilities. In the last decade, Chinese military and nuclear weapons capacities significantly advanced, boasting a sophisticated and expansive anti-access/area-denial (A2AD) ability. For U.S. tactical nuclear weapons to act as effective and credible nuclear deterrent, the weapons placed in Japan must have viable capabilities to penetrate the Chinese A2AD system. This means that the tactical nuclear weapons have to be survivable, credible, and also minimally politically damaging to the Japanese government. Therefore, Chinese military capabilities must be considered and assessed against any potential deterrence value of Japanese tactical nuclear sharing. To be a credible deterrent against Chinese aggression, Japanese tactical nuclear sharing must be able to credibly penetrate China’s A2AD capabilities. For instance, the People’s Liberation Army boasts robust anti-surface ship capabilities, including a vast arsenal of ballistic and anti-ship cruise missiles. China possesses roughly 60 launchers for surface-to-surface cruise missiles such as the CJ-10 and DF-100, which can reportedly target underground bunkers, naval ships, and land-based facilities. In addition, China reportedly possesses about 500 launchers in total for ballistic missiles such as DF-11, DF-15, DF-16, DF-21A, DF-21D, and DF-26. These capabilities can easily range the entirety of Japan and its surrounding waters. As a result, any tactical nuclear option reliant on surface ships, such as destroyers, would most likely prove vulnerable. Land Domain Possibilities When considering land-based tactical nuclear missiles, the expected and potential political implications and public backlash could make this option untenable. For example, if considering proximity and operation plannings, the missiles would be placed somewhere like Okinawa. Okinawans have been strongly promoting peace for decades. The tension between the Okinawa local government and the Japanese ruling party has been tense. This option will unlikely be accepted by the people and the government. Moreover, any land-based option will need multiple locations and expansive infrastructure to protect against Chinese long-range strike capabilities. The static bases for a land-based option will prove easy preemptive targets. Air Domain Possibilities In the air domain, Japan could leverage its growing inventory of F-35Bs which can be launched from the Izumo-class helicopter destroyers (DDHs), such as the JS Izumo and JS Kaga. F-35Bs are nuclear-certified, so Japan can theoretically receive the U.S. B61 tactical nuclear gravity bomb like the ones utilized by NATO. This would be the easiest option in terms of implementation. However, any counterstrikes carried out by F-35Bs will likely meet fierce resistance. The DDHs and their surface escorts could be easy targets for Chinese anti-ship capabilities. Additionally, given the relatively short range of 600 miles, an F-35B counterstrike requires substantial joint capabilities – such as air-to-air refueling, escorts, and more. Moreover, Chinese air defense systems – such as the HQ-22 and air defense capabilities of its surface fleet – may prevent F-35s from successfully penetrating Chinese A2ADs. Although this option provides the easiest implementation of tactical nuclear sharing, it faces significant operational challenges – undermining its strategic deterrence. Sea Domain Possibilities For Japan, nuclear-capable submarines provide the most resilient tactical nuclear sharing platform, given their survivability and asymmetrical advantage against Chinese A2AD capabilities. A handful of Japanese nuclear-capable submarines could penetrate China’s vaulted A2AD capabilities, which are optimized against surface combatants. In addition, Chinese anti-submarine warfare (ASW) capabilities remain an area of comparative weakness, which Japan should take advantage of. Modern submarines have enhanced stealth technologies and are built to be incredibly quiet. This is further enhanced by the fact that salt water is largely opaque to electromagnetic radiation. Moreover, the United States is also a leader in sub-launched missile technologies, ahead of China or Russia. As a result, Japanese nuclear-capable submarines could provide a tactical deterrent against Chinese aggression. For the purpose of tactical nuclear sharing, Japan does not need ballistic missile submarines or submarine-launched ballistic missile that carry intercontinental ballistic missiles. Japan could pursue nuclear-tipped Tomahawks. Obama in 2010 decided to retire the sea-based, nuclear-tipped Tomahawk cruise missiles (TLAM-N) to achieve his nuclear disarmament goals. At the time, this was a diplomatic reversal as Japanese officials previously requested the Obama administration to consult them on TLAM-N. The Japanese government believed TLAM-Ns to be essential for the credibility of U.S. extended deterrence. The Japanese doubted the U.S. commitment to extended deterrence and considered the possibility of decoupling. This episode demonstrates the importance of the TLAM-Ns to the Japanese perception of U.S. extended nuclear deterrence. At present, the Japanese government is accelerating its acquisition of land-based Tomahawk attack missiles. This political and policy embrace of Japanese strategic, long-range counter-strike capabilities may reflect a wider paradigm shift. This may reflect a growing political and public belief in the need to bolster Japanese deterrent capabilities in the face of a growing Chinese threat. For both F-35Bs and nuclear-capable submarines, any potential nuclear counterstrike would be carried out outside of the Japanese territory – unlike the land-based missiles. This could make it more politically palatable. Despite the difficult Japanese history with nuclear capabilities, TLAM-N may be a realistic evolution if the allies decided to pursue that course. However, this is not without its challenges. For instance, with TLAM-N retired, the United States has struggled to build its replacement, the Nuclear-Armed Sea-Launched Cruise Missile (SLCM-N). The Biden administration removed it from the FY2023 budget request despite the Trump administration’s insistence on reviving the capability. This has become a U.S. political conversation at the top of the budget and modernization effort issues. Japan currently does not have nuclear-capable submarines. However, if Japan decides to pursue U.S. nuclear sharing in the form of submarine-launched tactical nuclear weapons, then Japan could build its own nuclear-capable submarines and the associated infrastructure. While this will be cost-intensive, it would be a necessary requirement for credible nuclear sharing. The United States suffers from nuclear modernization and ship-building issues of its own – due to mounting costs and a scarcity of shipyards. After purchasing a few nuclear-capable submarines, Japan could learn how to build, maintain, and repair the submarines within the U.S. restrictions in Japan. Implications and Conclusion This article does not explore the complexities and various challenges Japan and the United States would face, if they were to implement nuclear sharing. The international reactions from both allies and adversaries will be critical. South Korea will likely ask nuclear sharing. The tension in the Indo-Pacific will rise tremendously. China and the DPRK’s reactions will be hostile. Nuclear sharing to Japan could trigger uncertain adversarial reactions. Pursuing nuclear-capable submarines and ports possible to host nuclear subs will be a costly option for Japan. However, this would be the most credible, survivable, and effective U.S. nuclear sharing option for Japan. If Japan and the United States were to agree on terms for nuclear sharing, then they could pursue both nuclear submarines and F-35B options simultaneously as implementations require significant time and money.